The present invention relates to a screen printing method in which paste such solder cream is printed on a work.
As a soldering method of electronic parts, a method by solder bump or solder pre-coating is known. In this method, on an electrode of a work such as electron parts or a substrate, a solder bump that is a protruding electrode of solder for soldering, or solder pre-coating that is solder coating is formed. As a solder supply method in this solder forming process, a screen printing is widely used. In this method, solder cream is printed on the upper surface of the work through a pattern hole provided for a mask plate.
Recently, fining of electronic parts is advancing, a pitch of electrodes formed in a work is also fined, and many electrodes are arranged at a high density. A mask plate used in order to form bumps on these electrodes is much smaller in mask thickness than a conventional mask plate used in solder printing on a print-circuit board. However, in case that the conventional screen printing method is applied intactly to screen printing which uses a mask plate having a thin mask thickness for the work in which such the electrodes having the high density are formed, the following problems are produced.
In order to secure good quality of printing in the screen printing, filling ability of surely filling solder cream in a pattern hole, and good plate separativeness in which the solder cream is separated from the pattern hole with its shape kept when the mask plate is separated from the work after the filling operation are required. However, as the electrodes are arranged at a higher density and the mask is made thinner, difficulty in printing is increasing. Particularly, it is very difficult to secure uniform and good plate separativeness throughout the entire surface of the work.